﻿412 Sir W. Ramsay and Dr. Spencer on Chemical and 



fact that it was present as a trisulphide, whereas all the other 

 elements were present as mono-sulphides; the additional 

 amount of sulphur prohably acting like the carbon in cast 

 iron. Tin sulphide was very probably mixed with tin oxide 

 and stannic sulphide, both o£ which would influence the 

 value obtained. We are proposing, at a later date, to make 

 a more thorough study of the action of ultraviolet light upon 

 compounds, both from the chemical and physical points of 

 view. Knoblauch made a series of measurements with sul- 

 phides ; from his results he attempted to prove that the whole 

 action is due to oxidation of the sulphides to sulphates, because 

 he could obtain no discharge with sulphates. He uses the 

 unipolar nature of the discharge to show that it must be a 

 case of oxidation ; against his theory is the fact that these 

 discharges occur equally well in an atmosphere of hydrogen. 

 The most oxidizable sulphide in Table VII. is probably that 

 of iron; and therefore, according to Knoblauch*, it ought 

 to give the most rapid discharge, which is not the case. 

 Again, if we take the iodides, Table VIII., they are not at 

 all easily oxidizable, yet copper and silyer iodides give quicker 

 rates of discharge than iron sulphide, and it is difficult to 

 imagine that they are more easily oxidized than any one of 

 the sulphides. The iodides are not in the same order as 

 either the sulphides or the metals ; they were prepared by 

 suspending plates of the metals over a dish of iodine until 

 the surface was coated with iodide. The plate was then 

 allowed to stand for some time, in order that we might have 

 a simple iodide, and not a solution of iodine in an iodide, 

 Many iodides could not be measured on account of their 

 deliquescence. The rate of discharge is calculated to the 

 same standard as in Tables V. and VII . 



Table VIII. 



Iodide of 



Rate of discharge. 



per cent. I in the 

 compound. 



Copper, Cul 2 



1240 81 tier cent. 



Silver, Agl 



1363 

 4145 



6280 

 7960 



56 „ 

 69 „ 

 68 „ 

 55 „ 



Cadmium, Cdl 2 



Tin, Snl 2 



Lead, Pbl 2 





With the exception of silver iodide, the only moniodide in 

 the series, the rates of discharge increase with increasing 

 percentage of iodine in the salt. The above experiments on 

 sulphides and iodides, together with those of Knoblauch, lead 

 to the conclusion that there is an emission of corpuscles from 



* Knoblauch, Zeitsch\f. Phi/sikalische Chemie, vol. xxix. p. 527. 



